In the prior art, air filtering apparatus of the type including an air filter housed in a dedicated cabinet are known for removing contaminants from air exhausted from a machine in an industrial setting. Referred to as cabinet collectors, such air filtering apparatus draw dirty air from a machine such as a saw, grinder, or other source of dirty air. A given cabinet collector is usually dedicated to a particular machine in a factory and substantially prevents the introduction of the generated contaminant into ambient air. Air flow through the machine and the cabinet collector is created by a motor/blower assembly which is housed within the dedicated cabinet.
As a cabinet collector is used to filter dirty air, contaminants become lodged on a surface of the filter media thereby increasing its flow resistance and reducing its overall effectiveness. In view of the fact that replacing the filter media on a regular basis would be prohibitively expensive, the filter media must be cleaned from time to time. While it is possible to enter the interior of the cabinet to manually clean the filter, it is recognized that it would be desirable to have effective automatic means for cleaning the filter element. One attempt to address the need for a self-cleaning cabinet collector is described in commonly assigned U.S. Pat. No. 4,443,235 to Brenholt et al dated Apr. 17, 1984. The Brenholt et al patent describes a frusto-conical filter element constructed from pleated paper filter media. By pleating a porous media a large amount of filtering surface can be placed in a small area. Thus, a filter made of a pleated porous media has a larger filtering surface than a conventional bay or pouch filter. To clean the pleated filter, the smaller axial end of the frusto-conical filter element is twisted about an axis co-axial with the conical axis of the filter element. After the smaller axial end has been twisted a predetermined amount, the end is suddenly released and the filter media suddenly returns to its original shape. The sudden return of the filter element to its original shape causes contaminants disposed on the filter media to become dislodged. An unfortunate consequence of the twisting of the filter element is that the resultant force on a given fold line of the pleated filter media includes a not insignificant "fold plane" component perpendicular to the fold line and perpendicular to the direction of spacing between adjacent pleats, as illustrated in FIG. 8B. This "fold plane" force component tends to collapse the pleat at the fold line. In fact, after a relatively small number of twists and releases, the pleats of the pleated filter media can collapse and seriously impair the cleaning effectiveness of the filter and its ability to "flex clean" itself upon the release of the twisting mechanism.